1. Field of the Invention
This invention relates to solid refuse disposal, and more particularly to a process in which oxygen-enriched gas is used to convert solid refuse in a vertical shaft to molten metal and slag, and an overhead gas having fuel value.
2. Description of the Prior Art
Anderson U.S. Pat. No. 3,729,298 describes a solid refuse disposal process which has as products a useful fuel or synthesis gas and an inert solid residue. The Anderson process involves the introduction of refuse into the top of a vertical refractory-lined furnace with the simultaneous introduction of an oxygen-enriched gas into the base of the furnace. The refuse forms a porous packed bed within the vertical furnace which can be analyzed in terms of three functional zones: a drying zone at the top section, a pyrolysis zone in the mid-section, and a combustion or melting zone (the hearth) at the base of the furnace. Apparatus useful for practicing the Anderson process is also described in U.S. Pat. Nos. 3,801,082 and 3,985,518 to Anderson.
As the refuse descends through the furnace under the influence of gravity, it is first dried by hot rising gases which are generated in the mid-section and hearth of the furnace. These gases are cooled as they give up their heat to the refuse. As the at least partially dried refuse descends further into the furnace, it is exposed to still higher temperatures resulting in the pyrolysis of the organic content of the refuse. During the pyrolysis phase, the combustible organic material is decomposed in the presence of a hot oxygen-deficient (reducing) atmosphere to a solid char residue and a gaseous mixture consisting predominantly of carbon monoxide, hydrogen and a variety of hydrocarbons. The gaseous mixture rises from the pyrolysis zone while the char and remaining non-volatile inorganic materials descend into the combustion and melting zone or hearth. In the hearth, the char, which is composed primarily of fixed carbon and ash, is reacted exothermically (combusted) with an oxygen-enriched gas.
The Anderson incineration system obviates many of the previous problems surrounding solid refuse disposal, in that the solid refuse conversion results in production of a useful product gas and a biologically inactive slag residue. Although the Anderson system is a substantial improvement relative to the prior art systems of solid refuse disposal, there are certain remaining problems relating to large scale use. If this system is operated in the conventional low pressure manner, high rate refuse processing requires a converter furnace diameter so large as to dictate field construction. Such field construction is not able to utilize the controlled fabrication methods available in factory construction and results in high construction costs. At the same time, operation of the conversion step at low pressure results in relatively high volume of overhead gases which also contributes to substantial equipment costs for the downstream cooling and cleanup processing. Another disadvantage of the low pressure conversion step involves the need for additional gas compression of the product fuel gas before it can be supplied for any use. This involves an additional piece of equipment and substantial energy which adds to the complexity and expense of the overall system.
Still another disadvantage of the prior art Anderson system is that although the refuse conversion produces the useful product fuel gas stream and the inert slag residue, it also produces a contaminated wastewater stream. The latter contains organic contaminants produced during the conversion step, and requires additional treatment such as discharging into an existing sewer system or construction of a separate wastewater treatment system. Such additional wastewater treatment systems have usually been of the biological treatment type such as the oxygen enriched aeration-activated sludge UNOX System developed by Union Carbide Corporation.
An object of the present invention is to provide an improved solid refuse disposal process of the vertical furnace type which is substantially smaller for a given throughput than heretofore required.
Another object is to provide an improved solid refuse disposal process which can provide the product gas at the desired consumption pressure without needing separate gas compression.
Still another object is to provide such an improved process requiring lower overall power consumption.
A further object is to provide a process having improved ultimate disposal of the liquid waste formed during pyrolysis of the solid refuse.
Other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.